The disaster was caused by cold weather. It affected rubber O ring seals in the rocket boosters of the Space Shuttle Challenger and this provoked them to weaken and fail.
Challenger's entire crew was killed when the shuttle exploded just 73 seconds after its launch, 46,000 feet in the air. The explosion was broadcast on live television.
The shuttle took off buoyed by hope and pride, watched by the entire nation including schoolchildren filling classrooms early in the morning.
There will be memorial services at Kennedy and Johnson Space Centers to remember the day and also a number of events all day long at the Challenger Learning Center.
Here's the disaster video of the Space Shuttle Challenger.